The present invention relates to a data processor for constructing a database of encoded moving picture signals, and a receiver which receives an output from the data processor.
The use of the original signals of picture signals, and particularly, moving picture signals increases the data amount. For this reason, before transmitting an original signal without any change or reading/writing it between storage media, the original signal is generally subjected to compression coding (to be simply referred to as coding hereinafter) to eliminate statistical and visual redundancies.
Usually, a picture signal thus encoded is transferred via a communication line or stored in a storage medium at a fixed transfer or read/write rate called an STM (Synchronous Transfer Mode).
In recent years, a new transfer method called an ATM (Asynchronous Transfer Mode) capable of instantaneously changing the transfer rate is becoming available. At present, however, STM service systems are always considered for communication application and storage application, and coding at the fixed rate is assumed to realize the quality of an encoded picture (to be simply referred to as a picture quality hereinafter) free from any practical problem.
FIG. 9 shows a conventional picture database. While a moving picture signal 1 input to the database is controlled with a parameter by a constant rate controller 2 so as to keep the transfer rate constant, the picture signal is encoded by an encoder 3 and stored in a storage medium 4.
As is well known, the special and time correlations between dynamic pictures often change locally, instantaneously, and abruptly. For example, the information amount generated by lossy coding generally called high-efficiency coding, such as H.261 serving as an international standard coding scheme for a video phone and a video conference picture signal, and MPEG-1 and MPEG-2 serving as international standard coding schemes used for the purpose of storage/communication/broadcast, greatly changes depending on the redundancy of an input picture.
To stably realize a high picture quality at a fixed transfer rate for various input pictures having different redundancies, the transfer rate must be fixed high, which is not a proper method in practice. At present, the picture quality is slightly sacrificed to fix the transfer rate lower and simplify the system configuration. For economical advantages, the rate to be fixed is set as low as possible.
A typical example of the transfer rate in the use of high-efficiency coding is a case wherein an NTSC color TV signal is encoded using MPEG-2 while maintaining a good picture quality. At this time, a proper transfer rate is said to be 6 Mb/s for each channel. At present, the digital television picture transfer technology is being introduced into satellite broadcasting, terrestrial broadcasting, a cable television, and the like, the transfer rate is one of the most important parameters in system design.
When coding at a fixed rate results in an insufficient picture quality, if the coding rate can be intermittently increased, a higher picture quality can be attained as a whole in many cases. Generally speaking, coding is usually performed at a fixed rate to output "main information", and when the picture quality is unsatisfactory with only the main information, "compensation information" that reduces a distortion caused by coding (coding distortion) is to be added, thereby greatly improving the picture quality.
One example of the prior arts employing this idea is "TV SIGNAL CODING EQUIPMENT" (Prior Art 1) disclosed in Japanese Patent Laid-Open No. 51-117820. According to this technique, as shown in FIG. 10, a temporarily encoded picture (encoded information e.sub.1) is decoded (into a decoded signal y') on the transmission side, a difference (coding distortion information e.sub.2) between the original picture (input picture signal y) and the decoded signal is also encoded and multiplexed with the main encoded information e.sub.1, and the obtained signals are transferred via a single transfer path. The coding distortion information e.sub.2 is "compensation information". On the reception side, the encoded information e.sub.1 is decoded into the decoded picture signal y', and compensation is performed based on the coding distortion information e.sub.2 to output a picture signal y". The degree of picture quality is higher in the order of y, y", and y'.
Another similar prior art is "CODING AND DECODING DEVICE FOR ANIMATING PICTURE SIGNAL" (Prior Art 2) disclosed in Japanese Patent Laid-Open No. 61-214885. Compared to Prior Art 1, this technique expands to a case using both motion-compensated interframe prediction and orthogonal transform.
In both Prior Arts 1 and 2, when the picture quality is unsatisfactory, "compensation information" is added to "main information" and transferred in order to reduce a coding distortion. However, to improve the picture quality improved as in Prior Arts 1 and 2 on the assumption of transfer by the STM as a general transfer form at present, the transfer rate must be determined on the basis of the information amount upon adding "compensation information", and a higher transfer rate is required.
In both Prior Arts 1 and 2, data generated by coding is formed as data in which "main information" and "compensation information" are integrally inseparable from each other. That is, the information made up of the two kinds of information corresponds to substantial "main information". For this reason, a database constructed by only conventional "main information" cannot be used without any change, and a database must be reconstructed with original picture signals.